The present invention relates to an apparatus and method for packing cigarettes into cigarette packs and sealing the packs with pre-applied adhesives. More particularly, the present invention relates to sealing cigarette packages in which the packaging stock, such as the pack labels, is coated with a dry adhesive before it is supplied to the packaging machine; the apparatus provides improved means for activating and for setting the adhesive.
Cigarette packing machines are widely used in high speed cigarette manufacturing operations. In typical commercial wet adhesive ("wet-glue") packing machines, cigarettes pass through successive processing steps in order to be formed into packs. A typical soft cigarette pack manufactured by such machines comprises an internal liner, an external label, which typically is made of coated paper, and a closure stamp. Water based or other solvent based or wax based adhesives are commonly used as adhesives to seal the packaging. Typically such wet glue is applied to the label at an edge corresponding to the sideseam of a cigarette pack and at another edge corresponding to the folded over bottom of the cigarette pack; the label is then wrapped around a bundle of cigarettes, usually 20 in number, that has already been wrapped in a foil liner. The wet glue is set by holding the label in place until the glue has dried. Heat may be applied in order to accelerate drying.
Wet-glue cigarette packers are widely known in the art of cigarette packaging. Exemplary versions of wet-glue packers are described in U.S. Pat. Nos. 3,628,309 and 3,948,115, both of which are assigned to G. D. Societa per Azioni, Via Pomponia 10, 40100 Bologna, Italy, which sells commercial wet-glue packers under various model designations, including GDX-1.
In addition to apparatus for the application of wet glue to the labels, the known wet-glue-type packers typically incorporate four processing turrets, each performing predetermined processing functions while passing cigarette bundles from turret to turret. The fourth turret functions first to finish the label folds on the bottom of the pack and then to set the glue on that bottom panel by operating in conjunction with a heating assembly having a flat raised portion designed to contact the pack bottoms and thereby set the glue by application of heat and pressure.
The known wet-glue-type packers also typically incorporate exit ramps, onto which the wrapped cigarette bundles enter after exiting the fourth processing turret. The exit ramp comprises a flat heater plate, a top pressure plate and conveying means, typically two conveyor belts. The heater plate and the top pressure plate operate in conjunction to set the sideseam glue as the cigarette packs are transported along the exit ramp by the conveyor belts.
Wet-glue packing machines possess a number of known disadvantages. Among these disadvantages are: slippage, which occurs when opposing portions of the packaging stock move with respect to each other before the wet glue is set such that the desired predetermined alignment is not achieved clogging, which occurs when the apparatus used to apply the wet glue becomes blocked or when wet glue causes the downstream processing apparatus to become clogged; and smearing, which occurs, for example, when glue seeps out from glued seams, when it bleeds through the stock, when it smears from its position or when it slings. Other disadvantages of wet-glue packaging machines are due to the following: product loss from machine stoppages for de-clogging or other maintenance, lack of flexibility regarding the placement of adhesive, difficulty in controlling the amount of glue that is applied, high viscosity of the glue itself, glue build-up along guides and frequent maintenance required by the glue application apparatus.
The invention disclosed in prior copending application Ser. No. 08/003,846 alleviates to a great extent the disadvantages of the prior art by disclosing cigarette packaging machines and methods that utilize packaging stock comprising a pre-applied adhesive to form cigarette packages that are sealed by activating the pre-applied adhesive. In one embodiment of that invention, packs are formed by wrapping labels having a pre-applied dry adhesive around a liner-wrapped cigarette bundle and then sealing the pack by activating the pre-applied adhesive, such as through the application of heat, and setting the adhesive, such as by cooling below the high activation temperature.
In an embodiment of the cigarette packer of the invention of copending commonly-assigned U.S. application Ser. No. 08/003,846, the exit ramp apparatus is split into heating and cooling zones to thereby effect the activation and setting of the sideseam seal. In that embodiment, after the packing machine is turned off, the machine continues to process packs that are then on the exit ramp apparatus so that all of the packs are processed and transferred from the machine and are not degraded by remaining on the heater. The many advantages of the invention of copending application Ser. No. 08/003,846 are discussed in that application.
One disadvantage of the known exit ramp apparatus is that the entire exit ramp is heated, typically to high temperatures, in order to activate pre-applied adhesive or to dry wet glue on the cigarette pack sideseam. It is desirable to be able to activate and set the sideseam seal at a temperature lower than previously required.
Another disadvantage is that the surface of the exit ramp is flat and is not uniformly heated, thereby creating non-uniform seals. Because the bottom plate is typically heated by heating elements underneath, the flat surface of the bottom plate may not be uniformly heated across its surface or from one end to the other. As a result, the cigarette pack label sideseams may not be uniformly sealed. It is desirable to be able to provide a more complete and uniform sideseam seal.
A further disadvantage of wet-glue packers is heat degradation or burning that occurs when packs remain on the heated exit ramp after the packer is shut off.